1. Field of the Invention
The present invention relates to monomer cast nylon and, more particularly, to monomer cast nylon having improvement in the antistatic properties and physical properties and a method of producing thereof.
2. Description of the Related Art
Monomer cast nylon (hereinafter referred to as "MC nylon"), which has a molecular structure belonging to Nylon 6's or Nylon 12's, is quite different from general nylon in that it is prepared through anion polymerization in the presence of a base catalyst in a casting mold. Generally, MC nylon has very high crystallinity, which provides superiority in tensile strength and abrasion resistance to other nylons. With these properties, MC nylon has numerous applications in various fields.
Lacking a function of removing electrostaticity, MC nylon itself is of electrical insulation with a volume specific resistance from 10.sup.14 .OMEGA..multidot.cm to 10.sup.15 .OMEGA..multidot.cm. It is virtually impossible to use MC nylon for fly wheels, jigs and pallets, which are required in fabricating or assembling processes of the fine electronic articles, such as printed circuit boards, LCD's and the like.
Metal powder, carbon black and graphite have been suggested to be incorporated in MC nylon to improve electrical conductivity. These conductive materials are added to melt-casting material monomers before polymerization. Metal powder, however, is now found to be unsuitable because it is deposited after casting. Carbon black, when added, exists in a paste form due to its large in specific surface area to adsorb a large quantity of material monomers, which inhibits the polymerization reaction of the monomers. Graphite, which has a smaller specific surface area than the carbon black, is readily dispersed in the monomers without a bad influence on the polymerization.
U.S. Pat. No. 5,179,155 to Sano, et al. discloses that the addition of graphite at amounts of 5 and 10% by weight resulted in volume specific resistance of 5.times.10.sup.8 .OMEGA..multidot.cm and 8.times.10.sup.7 .OMEGA..multidot.cm, respectively. In Sano, et al., however, when incorporating 2.5 wt. % of graphite, the volume specific resistance of the resulting MC nylon is 1.times.10.sup.11 .OMEGA..multidot.cm, which is too high to prevent static electricity. Sano, et al. note that the MC nylon has to incorporate at least 5 wt. % of graphite to have antistatic function. This requirement of at least 5 wt. % of graphite increases the production cost and may deteriorates intrinsic physical properties of MC nylon.
Moreover, Sano, et al. require that the graphite have a surface area of 10 m.sup.2 /g or loss in order to prevent the adsorption of the graphite to the monomers. Also the graphite has to be in a particle size of 5-25 .mu.m in order to prevent the agglomeration of graphite in the material monomer phase. The requirements for the surface area and the particle size are too limiting and may also increase the production cost.
There exist needs for development of MC nylon having an electrical conductivity level as that of a semiconductor (volume specific resistance of about 10.sup.6 .OMEGA..multidot.cm) while its physical properties are not degraded.